1. Field of the Invention
The present invention concerns a composite lead frame used for the packaging of a semiconductor device.
2. Description of the Prior Art
A composite lead frame used for packaging LSIs with 150 or more pins working at an electric power of 2 to 3 watt grade, such as gate arrays for CMOS or ECL having from several thousands to several hundreds of gates, includes a lead frame integrally formed with an island for mounting a semiconductor device and a plurality of leads extending outwardly from the island in which the island is formed greater than the size of the device, with an opening for a semiconductor device (hereinafter referred to as a device hole) being disposed at a central area on the surface of the island, and a polyimide film having a plurality of fine leads corresponding to the leads of the frame on the surface is bonded by means of an adhesive epoxy to the surface thereof. This intends to reduce the packaging cost by mounting LSI on a plastic QFP which is less expensive than PGA.
As LSIs have been increased in the degree of integration and made more versatile in the form in recent years, there has been an increasing demand for making the number of pins greater, reducing the size, increasing the operation speed and enhancing heat dissipation capability. and a composite lead frame can satisfy such requirements. However, in the conventional composite lead frame structure, bondability is poor as compared with conventional lead frames, lowering productivity. This is attributable to the soft and flexible nature of the material of an underlying substrate for the inner leads in a conventional composite lead frame comprising a polyimide film and an epoxy adhesive, which diffuses the bonding load and the ultrasonic power of the wire bonder toward the underlying substrate to worsen the bonding strength or homogeneity of the bonding of the wire.